Charging-free electron beam cure of dielectric material

ABSTRACT

An ultra low-k dielectric material layer is formed on a semiconductor substrate. In one embodiment, a grid of wires is placed at a distance above a top surface of the ultra low-k dielectric material layer and is electrically biased such that the total electron emission coefficient becomes 1.0 at the energy of electrons employed in electron beam curing of the ultra low-k dielectric material layer. In another embodiment, a polymeric conductive layer is formed directly on the ultra low-k dielectric material layer and is electrically biased so that the total electron emission coefficient becomes 1.0 at the energy of electrons employed in electron beam curing of the ultra low-k dielectric material layer. By maintaining the total electron emission coefficient at 1.0, charging of the substrate is avoided, thus protecting any device on the substrate from any adverse changes in electrical characteristics.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/013,799, filed Jan. 14, 2008 the entire content and disclosure ofwhich is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to methods of manufacturing asemiconductor structure, and particularly to methods of electron beamcuring of dielectric materials.

BACKGROUND

In advanced semiconductor chips operating at frequencies above 1 GHzrange, signal propagation delay between various devices or components inthe semiconductor chip accounts for a significant fraction of overallchip operation speed. The signal propagation delay in an interconnectstructure is dependent on an RC product of the interconnect structure,where R denotes the resistance of the interconnect wires and C denotesthe interconnect capacitance, or the overall capacitance of theinterconnect structure in which the interconnect wires are embedded. Thecontinuous shrinking in dimensions of electronic devices utilized inultra-large scale integration (ULSI) circuits in recent years hasresulted in increase in the resistance of the back-end of the line(BEOL) metallization as well as an increase in the intralayer andinterlayer dielectric capacitance. Thus, reduction of the resistance andthe capacitance of the BEOL metallization is paramount in enhancingperformance of the advanced semiconductor chips.

Use of copper instead of aluminum as the interconnect wiring materialfor the BEOL metallization has allowed reduction of the resistancecontribution to the RC product. Current focus in microelectronicsindustry is on reducing the interconnect capacitance by employing lowdielectric constant (low k) dielectric materials in the interconnectstructure of the advanced semiconductor chips, which typically contain amultilayered interconnect structure. While attempts to integrate variousmaterials having a low dielectric constant, commonly referred to as“low-k materials” in the art, have produced some successful results inthe art for materials having a dielectric constant of about 2.8 orgreater, integration of ultra low dielectric constant (ultra low-k)material into the BEOL metallization faces several significantchallenges.

Typical ultra low-k materials include various types of organosilicateglass (OSG), which contains Si, C, O, and H, and is oftentimes referredto as a SiCOH dielectric material. Efforts to integrate ultra low-kmaterials into BEOL interconnect wiring structures demonstrated that theultra low-k materials have a tendency to crack, especially at highhumidity environments. The driving force for cracking is inverselyproportional to the Young's modulus E, of the ultra low-k dielectric,and proportional to the square of biaxial stress applied to the ultralow-k dielectric material.

For small values of an applied stress tensor during elastic deformation,the magnitude of the strain tensor of an elastic solid is linearlyproportional to the magnitude of the stress tensor applied on it. Theratio of the stress to strain in the linear elastic region is known asYoung's modulus tensor, E, which is also known as the elastic modulustensor. The stress tensor, σ, the Young's modulus tensor, E, and thestrain tensor, ε, satisfy the following relationship: σ=E·ε. In general,the Young's modulus tensor, E, is a fourth order tensor with 81components, which can be reduced to 21 independent components for anyelastic material by considering symmetry and constraints on strainenergy. If the material is isotropic, the 81 components of Young'smodulus tensor, E, may further be reduced to the diagonal componentsthat have the same value, E, and some non-diagonal components with thevalue of the ratio of Young's modulus to Poisson's ratio ν, i.e., E/ν.Young's modulus, E, as the diagonal components of the fourth orderYoung's modulus tensor is commonly referred to, is a measure of thestiffness of a material, i.e., the higher the Young's modulus of amaterial, the stiffer it is, and the less strain it exhibits for a givenstress.

Increasing Young's modulus E and reducing the stress are very importantfor minimizing the cracking issue in low k dielectric layer. Whilestress is an external parameter generated as a function of geometryduring processing, Young's modulus E is a material property that may bemanipulated by subjecting the ultra low-k material to a suitabletreatment. By increasing Young's modulus E of the ultra low-k material,the strain of the ultra low-k material may be lowered for a givenexternal stress.

One way to increase Young's modulus E, i.e., the stiffness of a ultralow-k dielectric material, is to expose the ultra low-k dielectricmaterial to a beam of energetic electrons, i.e., an electron beam(e-beam) such as a flood electron beam. Such treatments are calledelectron beam curing. Electron beam curing usually results in asignificant increase of Young's modulus E and hardness in an ultra low-kdielectric material, which can then be integrated into BEOLmetallization structures with a reduced risk of cracking. Unfortunately,an electron beam treatment has undesirable side effects on front-end ofthe line (FEOL) devices, e.g., field effect transistors (FETs). Sucheffects include reduced break down voltage characteristics, largethreshold voltage shifts, and other adverse effects attributed tocharging of the substrate and various films on it, due to the electronbeam.

In view of the above, there exists a need for a method of electron beamcuring of ultra low-k dielectric material, while preventing any damagesor side effects on semiconductor devices located in the same substrate.

Further, there exists a need for a method of electron beam curing ofultra low-k dielectric material without inducing charging on thesubstrate containing the ultra low-k dielectric material and variousfilms and structures fabricated on it.

SUMMARY

The present invention provides a novel method and tool design thatalleviates the undesirable charging effects of e-beam curing, whilepreserving all its advantages, including increase in Young's modulus andhardness.

In the present invention, an ultra low-k dielectric material layer isformed on a semiconductor substrate. In one embodiment, a grid of wiresis placed at a distance above a top surface of the ultra low-kdielectric material layer and is electrically biased such that the totalelectron emission coefficient becomes 1.0 at the energy of electronsemployed in electron beam curing of the ultra low-k dielectric materiallayer. The shadowing effect of the grid of wires is compensated for bymoving the grid of wires to make an average dose of electrons uniformacross the ultra low-k dielectric material layer. In another embodiment,a polymeric conductive layer is formed directly on the ultra low-kdielectric material layer and is electrically biased so that the totalelectron emission coefficient becomes 1.0 at the energy of electronsemployed in electron beam curing of the ultra low-k dielectric materiallayer. By maintaining the total electron emission coefficient at 1.0,charging of the substrate is avoided, thus protecting any device on thesubstrate from any adverse changes in electrical characteristics.

According to an aspect of the present invention, a method for treating astructure with an electron beam is provided. The method comprises:

-   -   forming a dielectric material layer having a dielectric constant        of 2.7 or less on a substrate;    -   providing a grid of wires comprising a conductive material at a        distance from the dielectric material layer;    -   applying an electrical bias between the grid of wires and the        substrate; and    -   causing electrons to impinge on the dielectric material layer at        a predetermined energy, wherein the electrical bias is set at a        voltage at which a total electron emission coefficient from the        dielectric material layer is substantially 1.0 for the        electrons.

The dielectric material layer may be an ultra low-k dielectric materiallayer having a dielectric constant of 2.7 or less.

In one embodiment, the substrate remains substantially electricallyneutral while the treating of the structure.

In another embodiment, the dielectric material layer comprisesorganosilicate glass. The organosilicate glass may be non-porous, orporous and has a dielectric constant less than 2.5.

In even another embodiment, the method further comprises moving the gridof wires over the dielectric material layer at the distance, whereineach portion of the dielectric material layer is exposed to theelectrons at one point in time without being shaded by the grid ofwires. The motion may be a circular motion or an elliptical motionmaintained at the same distance from the dielectric material layer.

In yet another embodiment, the predetermined energy is from about 10 eVto about 100 keV.

In still another embodiment, the distance is from about 0.1 μm to about10 mm, and wherein the grid of wires comprises a plurality of wireshaving a diameter from about 1 μm to about 3 mm and separated by aspacing from about 3 μm to about 10 mm.

In a further embodiment, the method further comprises forming at leastone semiconductor device on the substrate prior to forming thedielectric material layer, wherein the substrate is a semiconductorsubstrate.

In a yet further embodiment, the method further comprises forming atleast one dielectric material layer and at least one metal interconnectstructure on the substrate, wherein the dielectric material layer isformed on the at least one dielectric material layer and at least onemetal interconnect structure.

According to another aspect of the present invention, another method fortreating a structure with an electron beam is provided. The methodcomprises:

-   -   forming a dielectric material layer having a dielectric constant        of 2.7 or less on a substrate;    -   forming a polymeric conductive layer directly on the dielectric        material layer;    -   applying an electrical bias between the polymeric conductive        layer and the substrate; and    -   causing electrons to impinge on the dielectric material layer at        a predetermined energy, wherein the electrical bias is set at a        voltage at which a total electron emission coefficient from the        dielectric material layer is substantially 1.0 for the        electrons.

The dielectric material layer may be an ultra low-k dielectric materiallayer having a dielectric constant of 2.7 or less.

In one embodiment, the substrate remains substantially electricallyneutral while the treating of the structure.

In another embodiment, the dielectric material layer comprisesorganosilicate glass. The organosilicate glass may be non-porous, orporous and has a dielectric constant less than 2.5.

In even another embodiment, the polymeric conductive layer comprisespolyaniline or polypyrole.

In yet another embodiment, the polymeric conductive layer has athickness from about 10 nm to about 1 μm.

In still another embodiment, the predetermined energy is from about 10eV to about 100 keV.

In a further embodiment, the method further comprises forming at leastone semiconductor device on the substrate prior to forming thedielectric material layer, wherein the substrate is a semiconductorsubstrate.

In an even further embodiment, the method further comprises forming atleast one dielectric material layer and at least one metal interconnectstructure on the substrate, wherein the dielectric material layer isformed on the at least one dielectric material layer and at least onemetal interconnect structure.

In a yet further embodiment, the dielectric material layer is formeddirectly on the at least one metal interconnect structure, and whereinthe dielectric material layer has a thickness from about 30 nm to about1 μm.

According to yet another aspect of the present invention, an apparatusfor electron beam curing of a target is provided, which comprises:

-   -   an enclosure for holding a vacuum environment therein;    -   an electron beam source located in the enclosure;    -   a chuck located on the enclosure; and    -   a grid of wires comprising a conductive material and located        between the electron beam source and the chuck, wherein the        target is mounted directly on the chuck, and wherein the chuck        and the grid of wires move relative to each other, while        maintaining a constant distance therebetween.

In one embodiment, an effect of shading of electrons impinging on thetarget by the grid of wires is rendered uniform across the target.

In another embodiment, the chuck is stationary relative to theenclosure, and the grid of wires moves relative to the enclosure.

In even another embodiment, the chuck comprises an upper chuck portionand a lower chuck portion, the lower chuck portion is stationaryrelative to the enclosure, and the upper chuck portion moves relative tothe enclosure.

In yet another embodiment, the grid of wires is stationary relative tothe enclosure.

In still another embodiment, the method further comprises:

-   -   a voltage feedthrough located on the enclosure; and    -   a conductive wiring between the voltage feedthrough and the grid        of wires, wherein an electrical bias is applied to the grid of        wires.

In still yet another embodiment, the conductive wiring is flexible.

In a further embodiment, the method further comprises a variable voltagesupply electrically connected to the grid, wherein a bias voltage on thegrid of wires relative to the chuck is capable of adjustment so that atotal electron emission coefficient from target is substantially 1.0 forelectrons impinging on the target.

According to still another aspect of the present invention, a system forelectron beam curing of a target is provided which comprises said targetand an apparatus, wherein the apparatus comprises:

-   -   an enclosure for holding a vacuum environment therein;    -   an electron beam source located in the enclosure;    -   a chuck located on the enclosure; and    -   a grid of wires comprising a conductive material and located        between the electron beam source and the chuck, wherein the        target is mounted directly on the chuck, and wherein the chuck        and the grid of wires move relative to each other, while        maintaining a constant distance therebetween;        wherein the target comprises a dielectric material layer having        a dielectric constant of 2.7 or less and located on a substrate;        and        wherein electrons emitted from the electron beam source impinges        on the dielectric material layer at a predetermined energy,        wherein an electrical bias is applied between the grid of wires        and the substrate, and wherein the electrical bias is set at a        voltage at which a total electron emission coefficient from the        dielectric material layer is substantially 1.0 for the        electrons.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the total electron emission coefficient of a typicalelectrically floating surface as a function of the energy of impingingelectrons in electron spectroscopy.

FIG. 2 is a vertical cross-sectional view of a first exemplary structureemployed in a first embodiment of the present invention, in which anelectrically biased grid of wires is placed over an ultra low-kdielectric material layer to alter the total electron emissioncoefficient of the ultra low-k dielectric material layer.

FIG. 3 is a top-down view of the grid of wires employed in the firstexemplary structure.

FIG. 4 shows a set of curves for the total electron emission coefficientof an electrically floating surface as a function of the energy ofimpinging electrons in electron spectroscopy for different electricalbias conditions on the grid of wires according to the present invention.

FIG. 5 is a first exemplary apparatus employing the first exemplarystructure according to the first embodiment, in which a biased grid ofwires moves above a dielectric material containing curing target at aconstant distance.

FIG. 6 is a second exemplary apparatus containing a second exemplarystructure according to a second embodiment of the present invention, inwhich an upper chuck portion moves relative to a lower chuck portion tohomogenize the effect of shading of a biased grid of wires.

FIG. 7 is a vertical cross-sectional view of a third exemplary structureaccording to a third embodiment of the present invention, in which anelectrically biased polymeric conductive layer located on an ultra low-kdielectric material layer is electrically biased to alter the totalelectron emission coefficient of the ultra low-k dielectric materiallayer.

DETAILED DESCRIPTION

As stated above, the present invention relates to methods of electronbeam curing of dielectric materials. It is noted that like andcorresponding elements mentioned herein and illustrated in the drawingsare referred to by like reference numerals.

In the past, electron beams have been used to charge conducting pads andvias in a ceramic package in order to test their electrical conductorcontinuity (J. M. Engel and F. E. Holmstrom J. Phys. D 3, 1505, (1970);J. M. Sebeson J. Vac. Sci and Technol. 6, 1060, (1973); Pfeiffer et al.J. Vac. Sci and Technol. 19, 1014, (1981); Lee et al. J. Vac. Sci andTechnol. B 9, 1993, (1991)). In one of the steps of this charging andtesting method, a conducting grid placed in the proximity of a samplesurface was used to induce repeatable charging of the sample. Accordingto the present invention, a conducting grid placed in the proximity of adielectric layer that is subjected to an e-beam cure is electricallybiased in order to ensure that the dielectric layer is not charged bythe e-beam, and as a result any damage caused by charging of a substratecontaining front-end-of-line (FEOL) semiconductor devices.

During e-beam curing of an ultra low-k dielectric material, electronswith energy from about 10 eV to about 100 keV, and typically from about250 eV to about 25 keV impinge on the ultra low-k dielectric material.The energy of the electrons depend on the thickness of the ultra low-kmaterial under treatment. Each electron has a probability of collisionwith atoms in the ultra low-k dielectric material, and thus generatingsecondary electrons (relatively low energy electrons) and backscatteredelectrons.

The physical principle of charging of a dielectric material layer by anelectron beam is directly linked to the total electron emissioncoefficient, σ, of the dielectric surface. The total electron emissioncoefficient, σ is the sum of the secondary electron emissioncoefficient, δ, and the electron backscattering coefficient η, i.e.,σ=δ+η.

Referring to FIG. 1, a typical total electron emission coefficient, σ asa function of incident electron energy is shown for an electricallyfloating surface. The general shape of the curve in FIG. 1 applies toboth conductors and insulators. When a material layer bombarded byelectrons is floating electrically, the material layer is chargednegatively when the energy of the incident electron beam (e-beam), E₀,is lower than a lower unit total electron emission coefficient energy E₁or a higher than a higher unit total electron emission coefficientenergy E₂ (i.e., when E₀<E₁ or E₀>E₂). This is because the influx ofelectrons into the material layer exceeds the emission of electrons fromthe material layer. When the energy of the incident electron beam isbetween the lower unit total electron emission coefficient energy E₁ andthe higher unit total electron emission coefficient energy E₂, (i.e.,E₁<E₀<E₂), the material layer is charged positively. This is because theinflux of electrons into the material layer is less than the emission ofelectrons from the material layer. When the energy of the incidente-beam E₀ is equal to E₁ or E₂, there is zero net charge added to thematerial layer. In this condition, the influx of electrons into thematerial layer matches the emission of electrons from the materiallayer, and there is no net change in the total charge in the materiallayer that is electrically floating. This phenomenon is judiciouslyutilized in this invention to reduce or eliminate charging in a materiallayer, and thus alleviate electrostatically induced damages tofront-end-of-line (FEOL) devices such as semiconductor transistors.

Curing of an ultra low-k material layer is effected by bombarding theultra low-k material layer with electrons having an energy optimized ata fixed value for specific desired properties of the ultra low-kmaterial layer as well as its thickness. Particularly, the energy of theelectrons is set such that the primary electrons, i.e., the electrons ofthe electron beam impinging on the ultra low-k material layer, penetrateall the way to the bottom of the ultra low-k material layer to ensurecomplete curing. In the prior art, it would only be a matter of chanceif the energy of the incident electrons was exactly the same as thelower unit total electron emission coefficient energy E₁ or the higherunit total electron emission coefficient energy E₂. While there would beno charging in this theoretical case, the probability of suchcoincidence is extremely low. Further, even if this was the case for oneof the layer thicknesses, layers with different thicknesses that areusually present in BEOL integration, would require different electronbeam energy than the lower unit total electron emission coefficientenergy E₁ or the higher unit total electron emission coefficient energyE₂. When a systematic method for preventing charging of multiple ultralow-k material layers is not provided, charging would inevitably occur,resulting in electrostatic damages to semiconductor devices underneaththe multiple ultra low-k material layers.

Referring to FIG. 2, a first exemplary structure according to thepresent invention is shown, which comprises a target 8 for electron beamcuring and a grid of wires 30. The target 8 comprises a substrate 10 anda back-end-of-line (BEOL) structure containing a dielectric materiallayer 26, a via level dielectric layer 22, a wire level dielectric layer24, metallization vias 21, and metallization wires 23.

The substrate 10 may be a semiconductor substrate, an insulatorsubstrate, or a metal substrate. In case the substrate 10 is asemiconductor substrate, the target 8 may further comprise at least onesemiconductor device such as a field effect transistor, a bipolartransistor, a capacitor, a resistor, a diode, etc. The semiconductorsubstrate may be a bulk substrate, a semiconductor-on-insulator (SOI)substrate, or a hybrid substrate having a bulk portion and an SOIportion.

The via level dielectric layer 22 and the wire level dielectric layer 24may comprise silicon oxide, silicon nitride, a dielectric metal oxide, aspin-on low-k dielectric material, or a low-k or ultra low-k dielectricmaterial such as porous or non-porous organosilicate glass. Themetallization vias 21 and the metallization wires 23 comprise aconductive material such as W, Al, and Cu, among which Cu is mostcommonly employed in advanced BEOL structures requiring highperformance. The metallization vias 21 and the metallization wires 23are formed in the via level dielectric layer 22 and the wire leveldielectric layer 24, respectively, by methods well known in the art. Thetarget 8 may comprise multiple levels of metallization vias 21 andmetallization wires 23.

The dielectric material layer 26 is located at the top of BEOL structureso that the surface of the dielectric material layer 26 is exposed. Thedielectric material layer 26 comprises a low-k material or an ultralow-k dielectric material. As defined herein, a low-k dielectricmaterial is a material having a dielectric constant less than thedielectric constant of silicon oxide, which is about 3.9. An ultra low-kdielectric material is a dielectric material having a dielectricconstant of 2.7 or less. Strictly speaking, ultra low-k dielectricmaterials are also low-k dielectric materials because a dielectricconstant of 2.7 or less is, by definition, less than the dielectricconstant of 3.9. Thus, an ultra low-k dielectric material is asub-category of the low-k dielectric material. Typically, ultra low-kdielectric material is a porous material. Some ultra low-k materials areporous versions of a non-porous low-k material having a dielectricconstant greater than 2.7.

Many low-k dielectric materials and ultra low-k dielectric material areknown in the art. An example of the low-k dielectric material is athermosetting polyarylene ether, which is also commonly referred to as“Silicon Low-K”, or “SiLK™.” The term “polyarylene” is used herein todenote aryl moieties or inertly substituted aryl moieties which arelinked together by bonds, fused rings, or inert linking groups such asoxygen, sulfur, sulfone, sulfoxide, carbonyl, etc. Methods of formingpores in a thermosetting polyarylene ether to form an ultra low-kdielectric material layer is also known in the art. Other examples oflow-k and ultra low-k dielectric material include porous and non-porousorganosilicate glass (OSG), which is also known as a SiCOH dielectricthat is deposited using the processing techniques disclosed inco-assigned U.S. Pat. Nos. 6,147,009; 6,312,793; 6,441,491; 6,437,443;6,441,491; 6,541,398; 6,479,110; and 6,497,963, the contents of whichare incorporated herein by reference. The organosilicate glass (OSG) maybe formed by providing at least a first precursor (liquid, gas or vapor)comprising atoms of Si, C, O, and H, and an inert carrier such as He orAr, into a reactor, preferably the reactor is a PECVD reactor, and thendepositing a film derived from said first precursor onto a suitablesubstrate utilizing conditions that are effective in forming the OSG.For example, the OSG may be formed by employing precursors such asmethylsiloxane, methylsilsesquioxanes, and/or other organic andinorganic polymer precursors. Such materials can be deposited by meansof spin-coating or Plasma Enhanced Chemical Vapor Deposition (PECVD).Other low-k and ultra low-k materials include fluorinated ornon-fluorinated organic polymer based low-k materials such asHoneywell's Flare™, polyimides, benzocyclobutene, polybenzoxazoles,aromatic thermoset polymers based on polyphenylene ethers.

Curing of the dielectric material layer 26 is especially effective whenthe dielectric material layer is an ultra low-k dielectric materiallayer having a dielectric constant of 2.7 or less, since ultra low-kdielectric materials are more prone to cracking under stress due totheir porosity. The dielectric material layer 26 is electricallyfloating relative to the rest of the target 30 since no electricalconduction path is provided within the dielectric material layer 26. Thethickness of the dielectric material layer 26 may be from about 30 nm toabout 1 μm, although lesser and greater thicknesses are explicitlycontemplated herein also.

A grid of wires 30 is provided over the top surface of the dielectricmaterial layer 26. The grid of wires 30 comprises a criss-cross mesh ofconductive wires, and is maintained at a constant distance Z from thetop surface of the dielectric material layer 26, which may be from about0.1 μm to about 10 mm, and typically from about 1 μm to about 1 mm. Aswill be discussed below, an electrical bias is applied between the gridof wires 30 and a conductive portion of the target 8, which is typicallythe substrate 10.

The target 8 and the grid of wires 30 are placed in a vacuumenvironment, and electrons provided by an electron gun and acceleratedby a predetermined voltage, which is determined by the thickness andmaterial of the dielectric material layer 26 as discussed above, impingeon the dielectric material layer 26. The grid of wires 30 comprises aconductive material such as metal. The electron gun may be an electronflood gun having a relative wide area for a cross-sectional area of thebeam. The diameter of the electron beam may be from about 0.1 mm toabout 100 mm, and typically from about 1 mm to about 10 mm. Typically,there is some shadowing of the impinging electrons by the grid of wires30 at any given moment, since the radius of each wire in the grid ofwires 30 tends to exceed the product of the distance Z between the topsurface of the dielectric material layer 26 and the grid of wires 30 andtypical angular spread in the direction of the electron beam.

Referring to FIG. 3, the grid of wires 30 is shown as seen from above,i.e., in the direction parallel to the electron beam. The diameter d ofeach wire in the grid of wires 30 may be from about 1 μm to about 3 mm,and typically from about 5 μm to about 100 μm. The spacing s betweenadjacent wires may be from about 3 mm to about 10 mm, and typically fromabout 15 μm to about 500 μm. The ratio between the diameter d of eachwire to the spacing s between adjacent wires may be from about 2 toabout 20, and typically from about 3 to about 6.

Referring back to FIG. 2, the energy of the electron beam may be fromabout 10 eV to about 100 keV, and typically from about 250 eV to about25 keV. If the position of the grid 30 relative to the target 8 isstationary, some areas of the dielectric material layer 26 would beshadowed from the impinging electron beam throughout the curing process.According to the present invention, however, the relative position ofthe grid 30 relative to the target 8 is changed to provide uniform doseof impinging electrons. Specifically, the grid of wires 30 over thedielectric material layer 26 moves relative to the target 8 at thedistance Z, which is held constant throughout the movement of the gridof wires 8 relative to the target 8. Thus, each portion of thedielectric material layer 26 is exposed to the impinging electrons atone point in time without being shaded by the grid of wires 30.

The relative motion between the dielectric material layer 26 and thetarget 8 may be a circular motion, an elliptical motion, or any motionconfined within a horizontal plane and designed to provide uniformexposure of all portions of the dielectric material layer 26 to theimpinging electrons. The relative motion is confined within a horizontalplane to insure that the distance Z between the top surface of thedielectric material layer 26 and the grid of wires 30 is maintainedconstant. The relative motion between the dielectric material layer 26and the target 8 may be effected by movement of the grid of wires 30,while the target is held stationary. An exemplary circular motion of thegrid of wires 30 is shown in FIG. 3. Alternately, the relative motionbetween the dielectric material layer 26 and the target 8 may beeffected by movement of the target 8, while the grid of wires 30 is heldstationary. Yet alternately, the relative motion between the dielectricmaterial layer 26 and the target 8 may be effected by a combination ofmovement of both the dielectric material layer 26 and the target 8.

Referring to FIG. 4, operation of the first exemplary structure isillustrated by a set of curves for the total electron emissioncoefficient of an electrically floating surface as a function of theenergy of impinging electrons in electron spectroscopy for differentelectrical bias conditions applied to the grid of wires 30 in the firstexemplary structure. A first curve 100A represents a total electronemission coefficient curve for a positive electrical bias on the grid ofwires 30, i.e., when a positive electrical voltage is applied to thegrid of wires 30. A second curve 100B represents a total electronemission coefficient curve for a negative electrical bias on the grid ofwires 30, i.e., when a negative electrical voltage is applied to thegrid of wires 30. A third curve 100C represents a total electronemission coefficient curve for a strongly negative electrical bias onthe grid of wires 30, i.e., when a strongly negative electrical voltageis applied to the grid of wires 30. Each of the first, second, and thirdcurves (100A, 100B, 100C) deviates from a total electron emissioncoefficient curve for a comparable surface without the applied biasvoltage, which corresponds to the curve of FIG. 1, i.e., the biasvoltage to the grid of wires 30 modify the total electron emissioncoefficient curve in certain ways.

While the details of the modifications to the total electron emissioncoefficient curve depends on the details of the first exemplarystructure including the material property and thickness of thedielectric material layer 26, physical dimensions of the grid of wires30, and the distance Z between the dielectric material layer 26 and thegrid of wires 30, qualitative features in the change is easilyidentifiable in each case.

In the case of the first curve 100A, the positive bias voltage on thegrid of wires 30 increases the total electron emission coefficientacross the incident electron energy range. The lower electron energy atwhich the total electron emission coefficient becomes substantially 1.0,which is herein referred to as a lower unit total electron emissioncoefficient energy under positive grid bias E_(1A), is less than thelower unit total electron emission coefficient energy E₁ without thegrid of wires 30. Likewise, higher electron energy at which the totalelectron emission coefficient becomes substantially 1.0, which is hereinreferred to as a higher unit total electron emission coefficient energyunder positive grid bias E_(2A), is greater than the higher unit totalelectron emission coefficient energy E₂ without the grid of wires 30.The dielectric material layer 26 charges positively when the energy ofthe impinging electron is between the lower unit total electron emissioncoefficient energy under positive grid bias E_(1A) and the higher unittotal electron emission coefficient energy under positive grid biasE_(2A) as electron deficit accumulates in the dielectric material layer26. Outside this range, the dielectric material layer 26 chargesnegatively as electrons accumulate in the dielectric material layer 26.At the lower unit total electron emission coefficient energy underpositive grid bias E_(1A) and the higher unit total electron emissioncoefficient energy under positive grid bias E_(2A), the dielectricmaterial layer 26 remains free of charging, i.e., remains chargeneutral.

In the case of the second curve 100B, the negative bias voltage on thegrid of wires 30 decreases the total electron emission coefficientacross the incident electron energy range. The lower electron energy atwhich the total electron emission coefficient becomes substantially 1.0,which is herein referred to as a lower unit total electron emissioncoefficient energy under negative grid bias E_(1B), is greater than thelower unit total electron emission coefficient energy E₁ without thegrid of wires 30. Likewise, higher electron energy at which the totalelectron emission coefficient becomes substantially 1.0, which is hereinreferred to as a higher unit total electron emission coefficient energyunder negative grid bias E_(2B), is less than the higher unit totalelectron emission coefficient energy E₂ without the grid of wires 30.The dielectric material layer 26 charges positively when the energy ofthe impinging electron is between the lower unit total electron emissioncoefficient energy under negative grid bias E_(1B) and the higher unittotal electron emission coefficient energy under negative grid biasE_(2B) as electron deficit accumulates in the dielectric material layer26. Outside this range, the dielectric material layer 26 chargesnegatively as electrons accumulate in the dielectric material layer 26.At the lower unit total electron emission coefficient energy undernegative grid bias E_(1B) and the higher unit total electron emissioncoefficient energy under negative grid bias E_(2B), the dielectricmaterial layer 26 remains free of charging, i.e., remains chargeneutral.

In the case of the third curve 100C, the strongly negative bias voltageon the grid of wires 30 decreases the total electron emissioncoefficient below 1.0 across the entire incident electron energy range.In other words, the strongly negative bias voltage suppresses the totalelectron emission coefficient below 1.0 irrespective of the incidentelectron energy. Thus, irrespective of the incident electron energy, thedielectric material layer 26 charges negatively as electrons accumulatein the dielectric material layer 26.

As can be seen from the characteristics of the response of the totalelectron emission coefficient curves, the incident electron energy atwhich the total electron emission coefficient becomes unity may bemodulated by the voltage bias to the grid of wires 30 relative to thetarget 8. The present invention takes a reverse approach and determinesthe incident electron voltage based on the details of the dielectricmaterial layer 26 such as composition and thickness. Thus, no compromisein processing details needs to be made, i.e., the incident electronenergy, dose, and angle of implantation may be set as needed based onthe physical and compositional characteristics of the dielectricmaterial layer 26. Once the incident electron energy is determined, thebias voltage to the grid of wires 30 is determined such that at thepredetermined incident electron energy, the total electron emissioncoefficient becomes unity. In other words, the voltage applied to thegrid of wires 30 is tuned to achieve an equal influx and total emissionof electrons from the dielectric material layer 26.

Referring to FIG. 5, a first exemplary apparatus containing the firstexemplary structure is shown. The first exemplary apparatus comprises anenclosure 90 for holding a vacuum environment therein, an electron beamsource 40 located in the enclosure 90, a chuck 3 located on theenclosure 3, and a grid of wires 30 connected to a variable voltagesupply 34 through a conductive wiring 31, a voltage feedthrough 32, andan external wiring 33. A target 8 containing a dielectric material layer(not shown) on the top surface is loaded onto, and fixed on, the chuck3. The target 8 and the grid of wires 30 collectively constitute thefirst exemplary structure shown in FIG. 2. The grid of wires 30 ismaintained at a constant distance Z over the top surface of the target8.

Electrons at a predetermined beam energy are emitted from the electronbeam source 40 and impinge on the target 8. An electrical bias voltagecalculated to induce a total electron emission coefficient of unity atthe predetermined beam energy according to the methods described aboveis applied to the grid of wires 30. The target remains free ofaccumulation of excess charge during the curing of the dielectricmaterial layer in the target 8.

While the electron beam impinges on the target 8, the grid of wires 30shades portions of the target from the electron beam as discussed above.The effect of shading of electrons impinging on the target 8 by the gridof wires 30 is rendered uniform across the target by a movement of thegrid of wires 30 relative to the target 8. In this case, the chuck 3 andthe target 8 remain stationary relative to the enclosure 90. The grid ofwires 30 moves relative to the enclosure 90. The conductive wiring 31 isflexible to continuously provide the electrical bias voltage to the gridof wires 30 during the movement of the grid of wires 30. The electronsmay impinge at normal incidence, or at a non-normal angle to the topsurface of the target 8.

The movement of the grid of wires 30 is limited to a plane parallel tothe top surface of the dielectric material layer within the target 8,i.e., the top surface of the target 8. The movement of the grid of wires30 may be characterized as a “2-axis wobble,” which moves the grid ofwires 30 in two directions by a distance that exceeds the diameter d ofeach of the wires in the grid of wires 30. Preferably, the distance ofthe movement is equal to, or greater than, the pitch of the grid ofwires 30. In this way, the “shadow” of the grid of wires 30 remains overa specific unit area of the top surface of the target 8 for a timeduration equal to that over any other similarly sized area of thesurface. Thus, the whole surface of the dielectric material layer isbeing cured to the same degree.

Referring to FIG. 6, a second exemplary apparatus containing a secondexemplary structure is shown. The second exemplary apparatus comprisesan enclosure 90 for holding a vacuum environment therein, an electronbeam source 40 located in the enclosure 40, a chuck 3 located on theenclosure 3, and a grid of wires 30 connected to a variable voltagesupply 34 through a conductive wiring 31, a voltage feedthrough 32, andan external wiring 33. A chuck 3 is provided on the enclosure 90 on anopposite side of the electron beam source 40. The chuck 3 comprises anupper chuck portion 4 and a lower chuck portion 2. A target 8 containinga dielectric material layer (not shown) on the top surface is loadedonto, and fixed on, the upper chuck portion 4. The target 8 and the gridof wires 30 collectively constitute the second exemplary structure,which is the same as the first exemplary structure shown in FIG. 2. Thegrid of wires 30 is maintained at a constant distance Z over the topsurface of the target 8.

Electrons impinge on the target 8 and an electrical bias voltage isapplied to the grid of wires 30 in the same manner as during theoperation of the first exemplary apparatus. The target remains free ofaccumulation of excess charge during the curing of the dielectricmaterial layer in the target 8.

The effect of shading of electrons impinging on the target 8 by the gridof wires 30 is rendered uniform across the target by a movement of thegrid of wires 30 relative to the target 8. In this case, the lower chuckportion 2 and the grid of wires 30 remain stationary relative to theenclosure 90. The upper chuck 4 moves relative to the lower chuck, andhence moves relative to the enclosure 90. The conductive wiring 31 may,or may not be, flexible since the grid of wires 30 remain stationary.The electrons may impinge at normal incidence, or at a non-normal angleto the top surface of the target 8.

The movement of the grid of wires 30 is limited to a plane parallel tothe top surface of the dielectric material layer within the target 8,i.e., the top surface of the target 8. The movement of the upper chuckportion 4 relative to the lower chuck portion 2 is a “2-axis wobble,”which moves the upper chuck portion 4 in two directions by a distancethat exceeds the diameter d of each of the wires in the grid of wires30. Preferably, the distance of the movement is equal to, or greaterthan, the pitch of the grid of wires 30. In this way, the “shadow” ofthe grid of wires 30 remains over a specific unit area of the topsurface of the target 8 for a time duration equal to that over any othersimilarly sized area of the surface. Thus, the whole surface of thedielectric material layer is being cured to the same degree.

Referring to FIG. 7, a third exemplary structure according to thepresent invention comprises a target 8′ comprising a substrate 10 and aback-end-of-line (BEOL) structure containing a dielectric material layer26, a via level dielectric layer 22, a wire level dielectric layer 24,metallization vias 21, and metallization wires 23, each of whichcomprise the same structural and compositional properties as in thefirst exemplary structure. Further, the third exemplary structurecomprises a polymeric conductive layer 70 formed directly on the topsurface of the dielectric material layer 26. The polymeric conductivelayer 70 comprises a conductive polymer such as polyanilline orpolypyrole, or any other polymeric conductive material containing C, O,H, and optionally N and/or S. The low atomic mass of materialscomprising the polymeric conductive layer 70 reduces probability of backscattering of the impinging electrons by the material in the polymericconductive layer 70. In other words, reduction in the potency of theimpinging electrons to cure the polymeric conductive layer 70 is onlyminimal since the atoms of the polymeric conductive layer 70 haverelatively low atomic mass unlike any transition metal. The thickness ofthe polymeric conductive layer 70 may be from about 10 nm to about 1 μm.

Electrical bias voltage is applied to the polymeric conductive layer 70relative to the conductive portion of the target 8′. Typically, theconductive portion of the target 8′ is the substrate 10. Compared to thefirst and second exemplary structures, the polymeric conductive layer 70is functionally equivalent to the grid of wires 30 in that theelectrical bias voltage applied to the polymeric conductive layer 70 isset at a voltage that renders the total electron emission coefficient ofthe target 8′ to be substantially 1.0 so that no net accumulation ofcharge occurs in the target 8′.

Unlike the first exemplary structure, the third exemplary structure isfree from non-uniform shading since the thickness of the polymericconductive layer 70 is uniform across the target 8′, and consequently,the reduction in flux of the impinging electrons is uniform across thetop surface of the dielectric material layer 26.

In one aspect, the third exemplary structure may be considered as alimiting case of the first exemplary structure. The polymeric conductivelayer 70 may be considered as a limiting case with regards to theproximity of a conductive grid of wires 30 to the surface in that thegrid of wires 30 physically contact the top surface of the dielectricmaterial layer 26 as shown in FIG. 2. Also, the polymeric conductivelayer 70 may be considered as a limiting case with regards to thediameter of wires in the grid of wires 30 in that the diameter becomesthin enough to pass the incident electrons, i.e., become“electron-transparent.” Further, the polymeric conductive layer 70 maybe considered as a limiting case with regards to the ratio of thespacing s between neighboring wires of the grid of wires 30 in that thespacing s shrinks to zero and the neighboring wires merge.

The contrast between the third exemplary structure and the firstexemplary structure is also noteworthy. The polymeric conductive layer70 abuts the dielectric material layer 26, while the grid of wires 30 isseparated from the dielectric material layer 26 as shown in FIG. 2.Relative motion between the polymeric conductive layer 70 and thedielectric material layer 26 is impossible, while relative motionbetween the grid of wires 30 and the dielectric material layer 26enables uniform dose across various portions of the dielectric materiallayer 26.

It is also noteworthy that the polymeric conductive layer 70 isconnected to the electrical bias voltage to set the total electronemission coefficient substantially equal to 1.0, i.e., unity, and not beelectrically connected to the conducting portion of the target 8′. Thedielectric material layer 26 serves as an insulation layer for thepurposes of electrical isolation between the polymeric conductor layer70 and conductive portions of the target 8′, which typically include thesubstrate 10 and the metallic structures such as metallization vias 21and metallization wires 23.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A method for treating a structure with an electron beam, said methodcomprising: forming a dielectric material layer on a substrate;providing a grid of wires comprising a conductive material at a distancefrom said dielectric material layer; applying an electrical bias betweensaid grid of wires and said substrate; and causing electrons to impingeon said dielectric material layer at a predetermined energy, whereinsaid electrical bias is set at a voltage at which a total electronemission coefficient from said dielectric material layer issubstantially 1.0 for said electrons.
 2. The method of claim 1, whereinsaid dielectric material layer is an ultra low-k dielectric materiallayer having a dielectric constant of 2.7 or less.
 3. The method ofclaim 1, wherein said substrate remains substantially electricallyneutral while said treating of said structure.
 4. The method of claim 1,further comprising moving said grid of wires over said dielectricmaterial layer at said distance, wherein each portion of said dielectricmaterial layer is exposed to said electrons at one point in time withoutbeing shaded by said grid of wires.
 5. The method of claim 4, whereinsaid motion is a circular motion or an elliptical motion.
 6. The methodof claim 1, wherein said predetermined energy is from about 10 eV toabout 100 keV.
 7. The method of claim 1, further comprising emittingsaid electrons in a flood electron beam from an electron flood gun. 8.The method of claim 1, wherein said grid of wires is provided in avacuum environment, and said method further comprises: providing a chuckwithin a vacuum enclosure; mounting a combination of said dielectriclayer and said substrate on said chuck; and providing a relativemovement between said chuck and said grid of wires by a horizontalmovement of at least one of said chuck and said grid of wires.
 9. Themethod of claim 8, wherein said horizontal movement is performed whilemaintaining a constant distance Z between an uppermost surface of saiddielectric layer and said grid of wires.
 10. The method of claim 8,wherein said providing of said relative movement comprises moving saidgrid of wires relative to said enclosure while said chuck is stationaryrelative to said vacuum enclosure.
 11. The method of claim 8, whereinsaid chuck comprises an upper chuck portion and a lower chuck portion,and said providing of said relative movement comprises moving said upperchuck portion relative to said enclosure while said lower chuck portionis stationary.
 12. A method for treating a structure with an electronbeam, said method comprising: forming a dielectric material layer on asubstrate; forming a polymeric conductive layer directly on saiddielectric material layer; applying an electrical bias between saidpolymeric conductive layer and said substrate; and causing electrons toimpinge on said dielectric material layer at a predetermined energy,wherein said electrical bias is set at a voltage at which a totalelectron emission coefficient from said dielectric material layer issubstantially 1.0 for said electrons.
 13. The method of claim 12,wherein said dielectric material layer is an ultra low-k dielectricmaterial layer having a dielectric constant of 2.7 or less.
 14. Themethod of claim 12, wherein said substrate remains substantiallyelectrically neutral while said treating of said structure.
 15. Themethod of claim 12, wherein said dielectric material layer comprisesorganosilicate glass.
 16. The method of claim 12, further comprisingforming at least one semiconductor device on said substrate prior toforming said dielectric material layer, wherein said substrate is asemiconductor substrate.
 17. The method of claim 12, further comprisingforming at least one dielectric material layer and at least one metalinterconnect structure on said substrate, wherein said dielectricmaterial layer is formed on said at least one dielectric material layerand at least one metal interconnect structure.
 18. The method of claim12, further comprising emitting said electrons in a flood electron beamfrom an electron flood gun.
 19. The method of claim 12, wherein saidpolymeric conductive layer comprises a conductive polymer selected frompolyanilline, polypyrole, and another polymeric conductive materialcontaining at least C, O, and H.
 20. The method of claim 12, furthercomprising applying an electrical bias voltage to said polymericconductive layer relative to said substrate.